Abstract

Conventional optical frequency synthesis suffers from a vast range of different oscillators involved,¹ ranging from micro wave to laser devices. We explore and demonstrate a novel technique based on di viding difference frequencies.² The arithmetic average f₃ of two laser frequencies f₁ and f₂ is generated by phase locking the second harmonic of f₃ to the sum frequency of f₁ and f₂:2f₃ = fi + f₂. Cascading of n stages obviously allows division by 2ⁿ. Phase comparison of an. initial difference frequency as large as a few hundred terahertz to a rf requires fourteen to sixteen stages, and an absolute frequency measurement is possible, if the initial frequencies f₁ and f₂ are phase related themselves, as, for example, a second harmonic and its fundamental wave.

© 1990 Optical Society of America